WhyApple's'iPhone6'CouldBeEvenThinnerThanPreviousModels

For the first time, Apple is using only one brightness enhancement film (BEC) in its backlit LCD display on the “iPhone 6.” This will allow the handset to be even thinner than previous models. Unfortunately, the move could also lead to early supply issues, according to China Times (via G for Games).
Enhancement film
The report notes:

Until now Apple and Miebea (the supplier) have used two BEFs, and delivering a new backlight with just a single brightness enhancement film can allegedly cause yield issues. To our understanding, the reason why a single BEF could cause yield issues is because the remaining layer needs to be better enough to get the job done by itself. As for the alleged yield problems, these reports suggest that some of Minebea’s backlight orders will be taken over by OMRON and Radiant.